In a single pressure switching chamber of the thermally-assisted puffer or self-blast types, the so-called thermal channel is a channel putting an arcing region into fluidic communication with a thermal volume or chamber.
During the initial stage of current interruption, as main contacts of the switching chamber separate and an electric arc is established between the male and female arcing contacts, the thermal channel provides a conduit for feeding hot gases from the arcing region, which is the volume between the male and female arcing contacts, into the thermal volume. The arc heats the insulating gas, such as SF6, between the contacts, and the heated gas is fed into the thermal volume in order to increase the pressure in this volume. This first phase is sometimes called the thermal volume pressurization phase. In a subsequent phase, the direction of gas flow in the thermal channel reverts and the previously stored insulating gas flows from the thermal volume into the arcing region through this channel. This action promotes the flow of insulating gas that transports heat away from the arcing region and provides adequate gas density and temperature across the arcing contacts to obtain successful interruption of an AC current after it decays to zero and in order for the gap to withstand the transient recovery voltage appearing across the switching chamber.
As is widely known, in a switching chamber of the thermally-assisted puffer type, a single volume or chamber plays the role of a compression volume, since gas inside this volume is pressurized by a moving piston or puffer, and the role of a thermal volume, since gas pressurization is increased by the arc thermal energy. In a switching chamber of the self-blast type, there are two distinct volumes or chambers, namely the thermal volume which is of fixed volume and which opens into the thermal channel, and the compression volume which is of variable volume and which is connected to the thermal volume through a valve.
In the present disclosure, the “thermal volume” can indifferently be the single volume of a thermally-assisted puffer type switching chamber or the so-called thermal volume of a self-blast type switching chamber.
The thermal channel is formed by the outer surface of the auxiliary nozzle and the inner surface of the main nozzle in the region between the thermal volume and the arcing region.
The shapes currently used for the thermal channel to achieve the 90 degrees turn from the longitudinal to the radial direction with respect to the switching chamber axis are simple arc segments with constant radius throughout the turn.
The applicant realized that such shapes are not optimal. In particular, the applicant found that these shapes lead to the formation of turbulence and eddies in the thermal channel which obstruct the insulating gas flow and reduce the efficiency of the pressurization phase of the thermal channel and of the subsequent injection of gas into the arcing region.
A purpose of the invention is to improve the thermal channel shape and in particular to reduce or even avoid the formation of turbulence and eddies in the thermal channel.